Third Generation Partnership Project (3GPP) specifications provide carrier aggregation (CA) for bundling multiple component carriers (CCs) to perform radio communications.
Carrier aggregation up to Long Term Evolution (LTE) Release 10 increases the throughput by simultaneously using multiple component carriers operated in a single evolved node B (abbreviated as “eNB” that stands for a base station).
In Release 12, “dual connectivity” is discussed, which technique expands intra-eNB carrier aggregation and achieves simultaneous communications using components carriers operated at different eNBs. See, for example, non-patent document 1 listed below. Dual connectivity corresponds to inter-eNB carrier aggregation and further improvement of the throughput is expected.
For example, when all the necessary component carriers are not accommodated in a single eNB, dual connectivity is an effective technique to achieve as high the throughput as in Release 10.
In intra-eNB carrier aggregation, a mobile station or user equipment (UE) configured with carrier aggregation is adapted to acquire broadcast information of the secondary cell (SCell) generally from the primary cell (PCell) through dedicated radio resource control (RRC) signaling. The SCell broadcast information contained in the RRC signals is the minimum required information for the UE that undergoes the carrier aggregation, namely the UE in the “RRC_CONNECTED” state, to transmit and receive data to and from the SCell. In other words, those information items unnecessary for carrier aggregation (e.g., information items used in the idle state) are not contained in dedicated RRC signals.
By acquiring SCell broadcast information through dedicated RRC signaling, the UE need not perform blind decoding on a physical downlink control channel (PDCCH) common search space on the SCell. This arrangement can reduce the processing workload and the power consumption at the UE.
The broadcast information of the PCell is acquired at the UE in the same manner as the ordinary communications process with no carrier aggregation set up. That is, a master information block (MIB) which is first read upon completion of cell search is acquired over a physical broadcast channel (PBCH), and the other system information items are acquired over a physical downlink shared channel (PDSCH). A system frame number (SFN) is contained in the MIB.
As illustrated in FIG. 1A, under intra-eNB carrier aggregation, component carriers (CCs) from cells of the same eNB are in SFN synchronization, operated at the same SFN timings. Upon receiving a PBCH from the PCell that supports CC#1, the UE 20 can know the SFN of the SCell and it is unnecessary for the UE 20 to receive a PBCH from the SCell.